Note: Descriptions are shown in the official language in which they were submitted.
~WO 94/06725 PCT/FI93/00363
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Method and apparatus for bending glass sheets
The present invention relates to a method for bending
glass sheets, said method comprising
- placing glasas sheets on a ring mould
- heating a glass sheet supported by the ring mould to a
bending temperature in successive heating stations
- preliminary bending of a glass sheet gravitationally
upon the ring mould
- final bending of a partly bent glass sheet in a bending
station by means of an overhead press-bending mould
while the glass sheet is still supported by the same
ring mould.
The invention relates also to an apparatus for bending
glass sheets. The apparatus includes an elongated furnace,
a number of ring moulds, a number of carrier wagons for
carrying the ring moulds through the furnace along a first
horizontal track, a bending station at the downstream end
of the furnace, and a hoist mechanism located below the
bending station for descending the wagon and a mould
resting thereon from said first track onto a second, lower
track.
US Patent publication 4,349,375 discloses an apparatus for
bringing a reshapeable vacuum mould from outside a furnace
through an opening in the furnace wall into the furnace.,
wherein a glass sheet is lifted from rollers by means of
the vacuum mould. After being bent with the vacuum mould
shaping, the glass sheet is descended onto a pick-up rim
brought thereunder for carrying the glass sheet to
tempering. Thus, the question is basically about other
type of technology than in the present invention, which is
based on supporting a glass sheet on a ring mould during
the course of heating and bending.
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The ring mould mould technique can be used for bending
simple bending shapes merely by gravitational bending.
More complex bending shapes can be produced with the ring
mould technique when gravitational bending is assisted by
using full-faced or partial-faced press bending moulds
approaching a glass sheet from above or below or from both
directions at the same time. US Patent publication
4,909,820 discloses an example of the case in which a
glass sheet is bent by means of a reshapeable ring mould
and the bending process is assisted by overhead partial-
faced press bending moulds. This arrangement involves e.g.
the following drawbacks. The press bending moulds
constantly present in a furnace complicate the assembly of
a heating resistance field above a glass sheet and also
screen the thermal radiation applied from heating
resistances to a glass sheet. In addition, the press
bending moulds heat too much and it is difficult to
provide them with mechanics that would withstand the
constant heat of a furnace. Therefore, the cited
publication US-4,909,820 proposes the use of a bending
station in which a glass sheet is not heated with an
overhead resistance field. This type of bending station
cannot be used for anything else but press bending; it
cannot be used for bending glasses with a traditional
method based on a ring mould and gravity without the use
of a press bending mould. After all, gravitational bending
requires that a glass sheet be heated while monitoring the
deflection of a glass sheet.
The Applicants' US Patent publication 4,497,645 discloses
a method and a furnace assembly for bending a glass sheet
gravitationally with a ring mould. The present invention
relates to a further development of this prior known
method and assembly in a manner that one and the same
apparatus can be used for effecting both press bending and
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traditional gravity-based bending with the same assembly
at the same bending location.
A second, alternative object of the invention is to
provide a press bending method and apparatus, facilitating
the flexible variation of bending shapes without
substantial production stops simply by replacing the press
bending mould with another one of a different shape. This
facilitates the use of lightweight, simple-design press
bending moulds, which need not be reshapeable.
These objects of the invention are achieved on the basis
of the characterizing features set forth in the appended
claims.
One exemplary embodiment of the invention will now be
described with reference made to the accompanying
drawings, in which
fig. 1 shows an apparatus of the invention in cross-
section at a bending station.
Fig. 2 is a schematical view of an apparatus of the
invention in vertical section, corresponding to a
furnace assembly disclosed in US Patent 4,497,645.
Fig. 3 is a schematical perspective view an apparatus of
the invention as viewed from the adjacent to
bending station, the walls being partially cut
away.
Fig. 4 is a view otherwise similar to fig. 3 but seen more
obliquely from above and provided with a store 26
for replaceable press moulds.
CA 02144066 2002-12-05
WO 94106725 PCT/FI93/00363
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The description and operating principle of a furnace
assembly shown in fig. 2 is disclosed in US Patent
publication 4,497,645. A
general furnace design is briefly described hereinafter -
with reference made to fig. 2. An elongated furnace 1 is
separated from its environment with thermally insulated
walls 24, serving as the ceiling, side walls and floor of
a furnace. The furnace includes an upper conveyor track 2
and a lower conveyor track 3 for carrying wagons 4
therealong. Each wagon 4 carries a bending mould 5 for
placing a glass to be bent thereupon. Extending downwards
from a thermally insulated furnace ceiling 24 at spaces
equalling the length of wagon 4 is a heat insulation 24,
the top edge of a front wall 8 extending to the level of
its bottom surface. When a wagon train on upper track 2
is at a standstill in a manner that said front walls 8 are
in line with heat insulations 24a, a separate heating
station 10 is formed at each wagon in the longitudinal
direction of a furnace. The ceiling of each heating
station 10 is provided with electric resistance elements,
the temperature of successive heating stations 10 rising
gradually when progressing towards the downstream end of
furnace 1.
At the downstream or outlet end of the furnace is a
heating and bending station 14, which is provided with an
elevator 6 for lowering wagons 4 from upper track 2 onto
lower track 3. The elevator 6 is preferably an articulated
jack. Alternatively, it is possible to employ horizontal
brackets mounted on vertical guides, as descrived in the
Patent application FI-915016. Elevator 6 is preferably
fitted with a thermally insulated floor 13. The end wall
of bending station 14 includes inspection windows 12 for
monitoring the bending of a glass sheet. In line with
windoows 12, said (rant wall 8 of each wagon is also
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provided with inspection windows 11. After bending a glass
sheet, said wagon 4 is transferred by means of elevator 6
from the upper onto the lower track for carrying wagons 4
in the opposite direction towards a loading station 15,
said wagon 4 advancing therein through a wagon opening 9.
After the replacement of glass, said wagon 4 is hoisted
with elevator 6 onto upper track 2.
The above-described construction and operation are prior
known from the Applicants' US Patent 4,497,645. A further
reference can be made to the Applicants' Patent
publication US-4,986,842, which discloses yet a few more
details in relation to this particular type of furnace.
This prior known type of furnace is well suitable for
bending windshields, a majority of which are still so easy
to bend that the bending can be readily effected by using
ring-mould bending gravitationally. Especially in
automobile industry, however, there is a clearly distinct
tendency towards more rounded and aerodynamic shapes. This
will lead to a requirement for bending biconvex, S-shapes
and other complicated shapes. This requirement cannot be
met with a sufficient manufacturing accuracy by a ring-
mould method based on gravitational bending. In order to
make a furnace assembly of the invention able to carry out
not only gravitational bending but also press-bending of
more demanding shapes, said bending station 14 is provided
with an arrangement described in more detail hereinafter.
An overhead press-bending mould 16, whose bottom surface
matches a desired final bending shape and is consistent
with the surface of a ring mould 5, is adapted to be
reciprocated in horizontal direction into bending station
14 and out of it into a thermally insulated space 23. For
this reciprocation, said mould 16 is mounted with a
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suspension bracket or pylon 17 on a wagon 18 running on
wheels 19 along a rail 20. The Rail 20 comprises e.g. a C-
profile, inside which said wagon 18 is movable. The flat
bracket or pylon 17 is able to travel in the slot of
profiled rail 20 as well as in a slot made in the top wall
of thermally insulated space 23. The thermally insulated
wall of space 23 is indicated by reference numeral 24'.
The wall of bending station 14 is provided with an opening
22' for moving said mould 16 in and out therethrough. The
horizontal portion of bracket or pylon 17 carries a wall
section 22 for closing said opening 22' when mould 16 is
in bending station 14. On the other side of mould 16, the
end of bracket 17a carries a wall section 21 for closing
said opening 22' after moving said mould 16 into space 23.
On the one hand, this arrangement is capable of preventing
the overheating of mould 16 and, on the other hand, the
excessive leakage of heat through the thermally insulated
walls 24' of space 23. This arrangement is necessary when
replacing moulds 16 of varying shapes in space 23 through
its openable floor gate 25. Below said gate 25 can be
located a conveyor track or a store 26 for a number of
different press-bending moulds 16. The bottom surface of
mould 16 must naturally correspond to the final top
surface shape of a ring mould 5 used at any given time.
The ring mould 5 comprises typically a hinged mould which,
through the action of weights 5a, pivots to its final
configuration while a glass sheet bends upon softening.
Fig. 3 illustrates in more detail the operating mechanism
of an articulated jack 6, comprising a crank gear 27
driven by a motor, not shown. A pin moving in a slot 20
turns an arm 28 rotating a shaft 30, which in turn pivots
the articulated arms of articulated jack 6. This type of
crank-arm drive provides a preferable moment curve a speed
control at critical shifting points so as to avoid
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excessive accelerations. In addition, the traveling
distance of mould 5 must be precisely controllable as it
approaches mould 16 during the course of press bending.
Operation of the apparatus proceeds as follows.
In loading station 15, a cold flat piece of glass is
placed on a ring mould supported by wagon 4. Wagon 4 is
forwarded onto upper track 2 and the glass sheet is heated
in successive heating stations 10. A final bending
temperature is not reached until in bending station 14,
whose ceiling is also provided with heating resistances
31. As the glass sheet reaches a temperature to begin its
gravitational bending, the bending process is monitored
through window 12. After reaching a certain degree of
bending, said articulated jack 6 is used for lowering
wagon 4 along with its mould 5 downwards a distance
sufficient for carrying mould 16 into bending station 14
along a horizontal track defined by transfer rail 20. Wall
sections 21 and 22 can be used for parking mould 16
precisely at a predetermined spot. Thereafter, said
articulated jack 6 is used for hoisting wagon 4 along with
its mould 5 upwards in view of effecting a press-bending
operation between moulds 5 and 16. Wagon 4 can be mounted
upon the floor of hoist 6 to be displaceable in such a
manner that the aligning equipment between moulds 16 and 5
are able to set moulds 16 and 5 accurately prior to final
press bending. Such aligning equipment may simply consist
of tapered pins and recesses or holes for centering the
pins while shifting mould 5/mould wagon 4. Alternatively,
provided there are no lateral clearances in hoist
mechanism 6, the alignment of wagon 4 can be done on top
of hoist mechanism 6.
After completing the press bending, said ring mould 5 is
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lowered down by means of hoist mechanism 6 and said press-
bending mould 16 is forwarded into space 23.
When the apparatus should be used for bending less complex ,
bending shapes solely by the application of gravity, said
press-bending mould 16 is retained in space 23 all the
time and the bending is effected as set forth in US Patent
4,497,645.
If the apparatus is used mainly for press bending and
various bending shapes are desired without substantial
production cuts, the opposite side of the bending station
can be provided with another space 23 with its press-
bending mould 16. Thus, the replacement of mould 16 can be
carried out on one side while the other side mould 16 is
in operation. A particular benefit obtained by a
production line of the invention is its flexibility in
terms of diversified production. This benefit has been
achieved in a mechanically simple manner by making use of
the lifting movement of hoist mechanism 6 for
reciprocating press-bending mould 16 along a horizontal
track.
Naturally, the invention is not limited to the above
exemplary embodiment but several structural details can be
modified within the scope of the annexed claims.
